A carbon material is generally and widely utilized as applications of a conductive material, a catalyst carrier, an absorbent, a separating medium, ink, tonner, and the like.
A nanocarbon material in nanometer size, such as a carbon nanotube and a carbon nanohorn aggregate, has come to attention in recent years with a focus on the characteristics as structures. Applications of a nanocarbon material have been intensively studied, as described in PTL 1 (carbon nanohorn), PTL 2 (drug delivery system (DDS)), PTL 3 (solid lubricant), PTL 4 (methane gas occlusion), PTL 5 (absorbent), PTL 6 (methane decomposition catalyst), PTL 7 (catalyst carrier), and PTL 8 (conducive material), for example.
In recent years, attempts have been made to provide functionalities, such as electrical conductivity, thermal conductivity, mechanical strength, electromagnetic shielding, and flame resistance, by adding a carbon nanotube to a matrix.
A technique described in PTL 9 disperses single-walled carbon nanotubes in an elastomer, thereby achieving high electrical conductivity and superior durability to repeated stress such as strain.
A technique described in PTL 10 adds a thermoplastic resin and organic modified layered silicate to a carbon nanotube, thereby achieving an electrically conductive thermoplastic resin and a plastic mold that exhibit superior electrical conductivity.
PTL 11 proposes a carbon nanohorn aggregate as a highly dispersive conductive material. According to a technique described in PTL 11, a superior conductive paste is implemented by mixing metal particles and a resin into a carbon nanohorn aggregate. The carbon nanohorn aggregate has a spherical structure on the order of 100 nm in which single-walled carbon nanohorns having a diameter of approximately 2 to 5 nm and a length of approximately 40 to 50 nm are radially assembled. Further, the carbon nanohorn aggregate differs from conventional spherical electrically conductive materials such as carbon black. A radial single-walled carbon nanohorn aggregate has many contacts with a matrix and has a characteristic of being easily entwined.
Further, there is a possibility that both of high electrical conductivity and high dispersibility may be achieved by mixing a highly dispersive spherical carbon nanohorn aggregate with a material having a needle-like structure with a large aspect ratio. In fact, efforts are being made to relax cohesion of carbon nanotubes to some extent and achieve high electrical conductivity by mixing single-walled carbon nanotubes and carbon nanohorn aggregates, according to a technique described in NPL 1.